Electromagnetic transducer motor



Nov. 11, 1958 J. E. VERARDO ELECTROMAGNETIC TRANSDUCER MOTOR Filed Feb.3, 1955 R O m E V m Jab/n E0 Verarda,

BY WW W M m D 8 6 4 Z ATTORNEY United States Patent Office 2,860,289ELECTROMAGNETIC TRANSDUCER MOTOR John E. Verardo, Massapeqna Park, N.Y., assignor to Fairchild Camera and Instrument Corporation, acorporation of Delaware Application February 3, 1955, Serial No. 485,948Claims. (Cl. 317-158) This invention pertains to transducer motors, andparticularly to improvements in the magnetic structure of anelectromagnetic transducer graving portion of a known form of facsimilereproduction machine. However, the improvement obtained by the presentinvention is also applicable to other devices in which uniformity anddependability of mechanical response to a given exciting current arerequirements.

The magnetic circuits of devices of this type, where the drivingcurrents are of alternating nature, and particularly where the currentsare of higher frequencies than normal power frequency, are generallymade up in laminated form, the magnetic material of each laminationbeing continuous in the intended direction of the flux therethrough. Theuse of such laminations, instead of a solid magnetically permeable body,inhibits the flow of eddy currents in directions cross-Wise of theintended flux direction, which eddy currents would otherwise represent apower loss and would produce heating of the iron. In addition, the useof relatively thin laminations effect a reduction in the hysteresis lossin the magnetic circuit, in accordance with well-known principles.

While the interface contacts between adjacent laminations of iron orsteel in themselves present a relatively high-resistance path to eddycurrents, due to poor facial contact as well as to the presence ofoxides of relatively high resistance on these faces, it has becomecommon practice to provide between the laminations a thin layer of anadhesiveinsulating material coated onto the thin magnetic sheets beforethey are assembled. This insulation is particularly required where thelaminations have been hydrogen-annealed, because the annealing processreduces any surface oxides which might have existed, and hence increasesthe surface conductivity between the laminations. Insulation is alsorequired where the magnetic material is inherently free of an oxidelayer. Since the insulating material is generally more or less plastic,it distributes the pressure of the assembly rivets or fasteners overwider areas of the laminations and is presumed to reduce the possibilityof slight changes in position of laminations during use. Of course, thebinding or adhesive effect of such materials inherently tends to makethe laminated assembly more unitary in action, and reduces internallocal vibration which would represent a further power loss.

In many applications, however, these measures have proved inadequate,especially where the transducer is one in which a relatively powerfulcurrent (perhaps of the order of an ampere) is utilized to produce amechan ical motion of the moving part which is measured in thousandthsof an inch. Such an application is represented by the output transducerof a known form of photo electrically controlled engraving machine, as awhole well described in U. S. Patent No. Reissue 23,914, issued December21, 1954 to J. A. Boyajean, Jr. as assignor to the owner of the presentapplication.

In that machine, the engraving transducer motor drives intended for usein the en- 2,860,289 Patented Nov. 11, 1953 a hot stylus into and out ofthe surface of an engravable sheet, at a fundamental frequency upwardsof 350 cycles per second. Commercial models of that invention utilizefrequencies as high as a thousand cycles per second or greater. However,the amplitude of motion of the engraving tool is quite small, being ofthe order of .015 inch or less. In order that the reaction between tooland material not affect the tool motion to a noticeable extent, it isnecessary to drive the tool with considerable force, and at thesefrequencies a highly efficient magnetic structure is required,especially for the magnetic circuit of the moving vane or rotor, as wellas one in which the excursion of the tool for a given energization ofthe transduccr shall be precisely controlled and accurately duplicated,not only over short periods of time, but over periods of several workinghours during which the ma chine is operating more or less continuously.The satisfactory accomplishment of this aim, which can be characterizedgenerally as an improvement in time and temperature stability, greatlyimproves the quality of the engraving produced, while minimizing thenecessity for attention by the operator and frequent readjustments. Theimportance of this inherent stability can be well realized when it isconsidered that a machine of this type is not working on a steady loadcycle, but instead has varying demands made upon it because of the tonedifference of the various kinds of copy which it is called upon toreproduce. It is important that the stability of the motor be such thatit performs the same whether it has been on for a short time or a longtime because, although a short time might be required for a one-columncut and a long time for a four-column cut, yet it becomes fairlyapparent that a short time is in effect only the initial part of a longtime. The quality of an engraving would be seriously impaired if themotor changed in performance after executing a part of the engraving.

According to the present invention, the problem is solved in a mostsatisfactory manner by the elimination of plastic or adhesive materialsfor binding the laminations of the magnetic rotor together, and thesubstitution of metallic interleavings in the nature of extremely thinlaminations of aluminum or an alloy of aluminum, combined with aparticular form of mechanical fastening for the laminations to maintainthe desired pressure through the stack or pile. Reduction of eddycurrents between laminations is accomplished by a simple anodizationwhich renders the surfaces of these aluminum shims nonconducting priorto assembly.

The invention will best be understood by referring now to the followingdetailed specification of a preferred embodiment thereof given by way ofexample, taken in connection with the appended drawings, in which:

Fig. 1 is an isometric view, with parts broken away, of a completetransducer motor in accordance with the invention,

Fig. 2 is an exploded isometric view of representative portions of themagnetic circuit of the moving vane, and

Fig. 3 is a graph showing the effect of the invention on the travel of astylus driving chuck in relation to the energizing current.

Referring now to Fig. l of the-drawings, the transducer motor itself isindicated generally by reference numeral 10, and is shown as mountedupon a base 12 by a pair of fiat leaf springs 14 so that the fore andaft positions of the motor 10 can be adjusted slightly with respect tobase 12 by means not shown. This slight movement is in the samedirection as the vibrating movement of the tool chuck 16, whichdirection is indicated by the arrow adjacent the arm 18 which carriesthe chuck. Insofar as the present invention is concerned, the main bodyof 'motor 10 may be considered stationary, the chuck and tool beingvibrated with respect thereto by reason of being connected to therotatable magnetic vane structure to be described.

The stator structure of the motor 10 comprises two stacks 2 and 22 ofC-shaped laminations of magnetic material such as a low-loss ferrousalloy. Since these stacks are stationary insofar as the transduceroutput is concerned; and since they are relatively large, they may bemade up by ordinary riveting together of the pre-' formed laminationswith or without the adhesive coating mentioned earlier. The statorstacks 2t} and 22 are rigidly clamped with respect to one another by endcastings 24 and 26 which are of box-like configuration and bolted to oneanother, as indicated at 28 by screws or bolts passing through thestator stacks. Both of these frames 24 and 26 are identical in shape,having a central rigid web 30 upon which webs are carried the respectiveend blocks 32 each having a shaft portion 34- between which shafts themoving vane 36 is mounted. Flanges such as 38 rigidly connect the innerends of the shafts 34 to the rotor assembly 36, so that slight rotarymovement of the vane is possible about the common axis of the shafts 34.While the motion is rotary, it is to be understood that no bearings areemployed, the slight motion permitted to rotor 36 resulting from torsionin the shaft elements 34.

Energizing coils 40 and 42 surround the vane structure 36 above andbelow its pivotal axis, these coils being wound to direct their fluxlengthwise of the laminations of the vane (that is, in the verticaldirection in Fig. l), and they are secured within the openings of theC-shaped stator laminations in any convenient way. Spacing strips 44 areindicated in Fig. 1 as wedged between the wrapped and insulated coils toforce them into the C-shaped openings of the stator bodies.

The action of a motor of this type is well described in the Boyajeanpatent mentioned above, and illustrated particularly in Figs. 3a and 3bof that patent.

A few of the laminations near the center of the stack comprising vane 36are extended upwardly from its general top surface, these extendedlaminations being riveted to the opposite sides of a block d6 which isintegral with the chuck driving rod 18. Thus, slight rotations of thevane or rotor 36 will produce the desired in and out movement of thetool chuck 16.

' When the rotor 36 is formed of magnetic laminations riveted to oneanother in a pile and with the usual cement or adhesive laminatedbetween them under heat and pressure, it is found that the position oramplitude of the chuck 16 is not uniquely defined by the energizingcurrent supplied to the coils 40' and 4-2 through their connecting leads48. Specifically, it has been noted that as the temperature of theentire motor varies due to heating effects of the coils, magnetizingcurrent and in accordance with the varying load cycles which itmust'perform, the amplitude of the tool motion is changed. While thechange is slight, it is sufiicient to affect adversely the quality ofengravings made with the device, particularly if this change occursduring some portion of a single engraving. In addition, at the higherworking temperatures, suitable cements tend to soften, so that the vane36 acts as a flexible body rather than as a rigid mass. Due to the factthat the cement represented a material which is basically elastic therewas a limit to the tightness of a stack. Obviously if there were cementbetween the laminations the rivets, unless they squeezed out all thecement, would not create the maximum tightness that could be obtained.in an actual embodiment, the shaft portions 34 may be each about a halfinch long and about a quarter inch in diameter. Such a steel shaft is ofcourse extremely rigid, and for accurate results it is essential thatthe rigidity of the rotor 36 carried by these torsion shafts shall notbe impaired. It was also noted that erratic performance of the rotor 36resulted from the fact that repeated fiexures of the armature 9.11

' the improved arrangement of this invention, in which the vane 36caused the headed pins or rivets holding them together to become loose,permitting greater motion of the tool than called for by the signalinformation applied to the energizing coils. It is apparently impossibleto provide permanent rigidity by a riveted structure of this kind overlong periods of time.

The present invention overcomes the defects of prior constructions byeliminating all non-metallic materials in the rotor, and specifically byeliminating the resin, cement and other material formerly used betweenthe adjacent ferro-magnetic laminations. Instead the invention utilizesbetween each two adjacent laminations a thin shim of aluminum oraluminum alloy, formed to the same shape as the ferrous laminations buthaving a thickness of the order of only one and one-half thousandths ofan inch. These aluminum shims are anodized to ten der the surfacesnon-conducting before assembly, and when the stack of inter-leavedmagnetic laminations and shims is assembled, taper pins are driventhrough the aligned apertures in the stack, and at least the small endof each taper pin is headed over to complete the assembly. This headingover of the taper pin removes any possibility of the taper pin becomingloose.

Fig. 2 shows very clearly the assembly of the rotor structure. In thisfigure, a pair of adjacent low-loss iron alloy laminations are indicatedby numerals 50, and between then is shown one of the anodized aluminumshims 52. Each of the elements has aligned holes to receive the assemblyfasteners. These are tapered pins of which two designated 54 passthrough the laminations as well as the end plates or flanges 38 integralwith the shaft elements 34, while the two pins connecting the outer endsof the laminations only are designated 56. Preferably, the taper ofsuccessive pins vertically of the assembly is reversed, so that if onepin increases in diameter from left to right of the stack, the next onewill increase from right to left and so on. At least the smaller end ofeach taper pin is headed over after assembly, and the larger end may beleft alone or preferably pressed against the last lamination through awasher which is sized to ensmall, corresponding to the standard 2/0machineryv taper pin of hardened steel, for a stack assembly having awidth across laminations of one inch and comprising fifty-nine magneticlaminations of .015 inch thickness, and fifty-eight anodized aluminumshims having .0015 inch thickness.

The improvement in stability and the ability to duplicate movement ofthe tool chuck is indicated graphically in Fig. 3 of the drawings, whichshows curves relating the chuck motion in thousandths of an inch to thesignal current in the coils expressed in'amperes. The dashed curve A hastwo legs, the upper one indicating displacement of the tool or chuckmeasured with the amplitude going to higher valves, and the lower curvegiving the displacement with the amplitude decreasing. This doublevaluedcurve clearly indicates the lack of reproducibility of displacements forgiven signal currents. The solid straight line curve B represents theresults obtained with position of the chuck is linearly relatedto theenergizing current, and regardless of the direction of amplitude change(increasing or decreasing) of the chuck when the measurement is made.Moreover, the relationship is practically invariable with time andtemperature of the motor, as has been demonstrated in operating testsextending over as much as eight hours of operation at maximum signallevel. There is no warm-upfrequired for this motor. Whether theoperating time is zero plusone unit of time or zero plus units of time,the performance remains the same.

It is presumed that the use of the aluminum shims provides greatlyimproved frictional contact between, successive laminations by virtue ofthe higher clamping pressure that could be used, and that the use oftaper pins rather than straight shank fasteners provides continuoustight bearing surfaces between the laminations and the pins. Theelimination of all non-metallic materials is believed to be responsiblefor the greatly improved time and temperature stability of the motor,and its complete freedom for mechanical hysteresis effects. The maximumtightness of a stack was heretofore limited by the use of cement. Theelimination of all non-metallic elements removes any upper limit to thetightness of a stack. By the use of suitable clamping devices it ispossible to achieve as near to solid stack tightness as is possibleWithout in fact making it a solid stack.

The elimination of any non-metal material also removes any heatinsulation efrects that existed. The heat transfer ability of the unithas been improved with the result that the motor heat rise is less.

To recapitulate, the invention provides a mechanically solid magneticstructure of high stability and good eddy current insulation, togetherwith excellent thermal conductivity nearly equivalent to that of a solidblock of metal. The resulting improvement in heat dissipation, and inthe position stability of the driven element, eliminates some of thepower losses heretofore experienced, and in many cases provides betterposition stability with a smaller restoring force (torsion barcross-section) which again may effect a substantial reduction in therequired power input.

While the invention has been described herein in connection with itsapplication to a transducer motor to which extremely rigorous dutycycles are applied, it is obvious that the principles of the inventionmay equally well be applied to other magnetic structures in whichreproducibility of position is essential. Hence, the invention is not tobe limited to the details specified above except as may be required bythe scope of the appended claims.

What is claimed is:

1. A rotor for electromagnetic chuck drive transducers, comprising aplurality of low-loss magnetically permeable laminations, shims of thinductile aluminum sheet stock having anodized surfaces interposeddirectly between each pair of successive laminations, end plates forsaid rotor, and tapered pins passing through said laminations, shims andend plates and headed over to secure the same in rigid face to facecontact, and an output stub shaft secured at one of its ends to at leastone of said end plates.

2. In an electromagnetic transducer, a vibrating element comprising aplurality of thin, low-loss magnetically permeable metallic laminations,shims of relatively thinner ductile metallic sheet material interleavedbetween the successive laminations, the shims being anodized to formintegral electric insulating layers on their opposite surfaces, andmeans for clamping the interleaved laminations and shims tightlytogether in immediate face contact to form a structure which willmaintain its rigidity under vibration even at elevated temperatures, andan output stub shaft secured at one end to said element and lyingperpendicular to the planes of said laminations.

3. The invention in accordance with claim 2, in which the clamping meanscomprises a plurality of tapered pins passing through said laminationsand shims and headed to secure the latter together.

4. In an electromagnetic transducer, a vibrating element comprising aplurality of thin, low-loss magnetically permeable metallic laminations,shims of relatively thinner ductile metallic sheet material interleavedbetween the successive laminations, the shims having integral electricinsulating layers on their oposite surfaces, and means for clamping theinterleaved laminations and shims tightly together in immediate facecontact to form a structure which will maintain its rigidity undervibration even at elevated temperatures; the thickness of said shimsbeing of the order of one-tenth the thickness of said laminations, andan output stub shaft secured at one end to said element and lyingperpendicular to the planes of said laminations.

5. The invention in accordance with claim 4, in which said shims aresurface-anodized aluminum sheet material.

References Cited in the file of this patent UNITED STATES PATENTS420,396 Thomson Jan. 28, 1890 448,644 Farmer Mar. 24, 1891 1,782,521Trombetta Nov. 25, 1930 1,877,569 Falkenthal Sept. 13, 1932 2,410,220Langworthy Oct. 29, 1946 2,506,637 Fog May 9, 1950 FOREIGN PATENTS136,745 Switzerland Feb. 1, 1930

